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Beam Diagnostics Using Synchrotron Radiation:
Theory and PracticeUS Particle Accelerator School
University of California, Santa Cruz
San Francisco — 2010 January 18 to 22
Pinhole Cameras – Operation and Analysis
Jeff Corbetta, Alan Fishera, Walter Moka, Weixing Chengb
a - SLAC National Accelerator Laboratoryb - Brookhaven National Laboratory
• Low-emittance beam at 3rd generation light sources and HEP accelerators (ILC damping ring, superB, ERL, SLS /SOLEIL /Diamond /SSRF /ALBA /PETRA-III /NSLS2 etc…)
• Horizontal emittance ~ 1 nm.rad, vertical emittance ~ 10 pm.rad
• Typical beam size < 10um vertically (100um horizontal)
• Q: How to measure such a small beam?– Visible light image of synchrotron radiation (diffraction > 50um)
– Wire scan, laser wire (minutes for a full scan, 1-D)
– Interferometer (~10um resolution)
– Vertical beam size from p-mode radiation
– X-ray pinhole (simple, ~5um resolution)
– Fresnel zone plate (x-ray imaging of monochromatic beam, used at ATF, Spring-8 etc.)
– X-ray refractive optics (monochromatic light, complicated)
Small beams need to be measured
Jan/18/2010 2Pinhole Cameras – Operation and Analysis
First Observation of Pinhole Image
Jan/18/2010 3Pinhole Cameras – Operation and Analysis
“景到（倒），在午有端，与景长，说在端” 《墨经》
The image is upside down, because of the pinhole in the wall.
墨子 (468-376 B.C.)
Camera Obscura
Jan/18/2010 4Pinhole Cameras – Operation and Analysis
object
imagepinhole
d1 d2
1
2d
dM
X-ray Pinhole Camera - Schematic
Jan/18/2010 5Pinhole Cameras – Operation and Analysis
SPEAR
Soleil
SPEAR3 Pinhole, Filters, YAG Screen and Camera
Jan/18/2010 6Pinhole Cameras – Operation and Analysis
SPEAR3 pinhole results
Jan/18/2010 7Pinhole Cameras – Operation and Analysis
x-position [mm] x-position [mm]in
tensity [
au]
inte
nsity [
au]
Measurement Theory
Three optics available:
– Low emittance
– Achromatic
– Low-alpha
22
E
Exxx
yyy 2
BESSY-II Pinhole Array
Jan/18/2010 8Pinhole Cameras – Operation and Analysis
Constant Image Intensity
Fin
ite
be
am
div
erg
en
ce
Used at ALS and ASP as well
Beam size & divergence
Optimize the pinhole size
Jan/18/2010 9Pinhole Cameras – Operation and Analysis
If the pinhole is large, ray-optic „spread‟ dominates
d1 d2
w
1
)21
(
d
ddw
If the pinhole is small, diffraction dominates...
Geometric error
Diffraction error
Other measurement errors include: Screen, CCD camera and
chromatic error etc
Optimize the pinhole size (cont’)
Jan/18/2010 10Pinhole Cameras – Operation and Analysis
2222
ndiffractioblursourceimage M
1
21
2 L
LLwblur
p
w
Lndiffractio
2
4
12
p
L1 Distance from source point to pinhole
L2 Distance from pinhole to screen
M=L2/L1, magnification factor
W pinhole size
~ 40 mm
Optimize the pinhole size (cont’)
Jan/18/2010 11Pinhole Cameras – Operation and Analysis
Geometric error:
Diffraction error:
SRW PSF simulationa – pinhole width
d – distance from source point to pinhole
D – distance from pinhole to screen
E – photon energy in eV unit
Different curve corresponding to different filters
‘Polychromatic’ Diffraction
Jan/18/2010 12Pinhole Cameras – Operation and Analysis
Integrate intensity pattern over photon spectrum
spectrum at screen
dN/dE: Photons/sec/keV
Sands-121
C. Limborg - SSRL
PSF Calculation
Jan/18/2010 13Pinhole Cameras – Operation and Analysis
Ay=40 micron
(optimum)
Ay=5 micron
(diffraction)Ay=250 micron
(geometric)
143mm 250mm78mm
J. Bergstrom - CLS
Putting it all together…
fresnel.m valid from geometric to diffraction regimes
SRW, SPECTRA etc. can do the similar job
Phosphor screen error
Jan/18/2010 14Pinhole Cameras – Operation and Analysis
Diamond, screens compare
Power phosphor screen YAG
To select the screen:
– Spatial resolution
– Time response (decay time,
70ns for YAG:Ce)
– Photon yield of the screen
– Emission wavelength
– Radiation damage etc.
CCD error
Jan/18/2010 15Pinhole Cameras – Operation and Analysis
CCD – Charge Coupled Device
Finite pixel size (Flea2, 4.65 x 4.65µm pixel size)
Spilling to neighbors due to spilled charge or scattered radiation
][,_3.0 pixelsfractionspillccd Screen and CCD errors are negligible if the pinhole magnification
factor is large
Summary
Jan/18/2010 16Pinhole Cameras – Operation and Analysis
- Pinhole cameras effective in the x-ray regime (~5mm resolution)
- System construction fairly straight-forward
- Power loading considerations
- Optimize aperture size
- Data analysis relies on comparison of model with measurement
fresnel.m
- Relative high exposure time due to small aperture (fast measurement
needed for injection transient and machine physics)
